Voltage regulator for generators



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Feb. 5, 1963 l H. K. sEIKE 3,076,922

VOLTAGE REGULATOR FOR GENERATORS- 2 Sheets-Sheet 1 .FIQ' .1

-Filed April 18, 1960 3a 36 46 4a 50 INPUT K VOLTAGE POWER FILTER SSNASG'G AMPL'F'ER SwITOH CL'PPER 4 A II I l II IIE 40 I 44 52 REFERENCE *SUPPLY TEMP. AMEIENT BACK- vOLTAGE VOLTAGE STABIUZER CONTROL TEMP. BIAS 4 lo 34 /2 DELAY l l 24 VOLT A STAGE BATTERY I I l l I /4 To VER/OLE ELECTR/c/IL Sg' SYSTEM (f) I- Z Z 0W BATTERY OUTPUT,- .FI 613A fr REA w GENERATOR .Lo/I0 5 IOO o A VER/16E BA TTERY OUTPUT,-

.16.38 A VER/16E GENERATOR OAD f//GH RA TTERY OUTPUT,- .FI (1'. 30 L/GHT GENERATOR LOAD INVENTOR. O 50 |00 |50 He/mui' K'. ,ezlfe wAvEI-ORMS OF OOLLEOTOR-EMITTER Hyg 4, MAQMQMA VOLTAGE ACROSS POWER TRANSISTORS /f y Feb. 5, 1963 H. K. sElKE VOLTAGE REGULATOR FOR GENERAToRs 2 Sheets-Sheet 2 Filed April 18, 1960 Nevada Filed Apr. 1S, 195?, Ser. No. 22,846 15 Claims. (El. S22-28) This invention is directed to voltage regulators and more particularly to a transistorized regulator system which senses the voltage level of a direct-current (D.C.) source and provides a supplemental voltage for boosting or supplementing the source voltage, thereby furnishing an output potential which remains constant notwithstanding variations of the source voltage.

There has long been a need for reliable, portable and light-weight power supplies which provide a precise output potential for use, by way of example, in certain automotive or other types of mobile vehicles, to afford precision operation `of electrical equipment carried by the vehicle.

With the advent of economical, small and highly reliable transistorized converter systems such as that described and claimed in applicants copending application entitled Static Constant Voltage D.C. to D.C. Converter, tiled January 28, 1960, having Serial No. 5,184, and assigned to the assignee of the present invention, the Iutility of such a well regulated power supply as is provided with the present invention is even more apparent. The converter shown in the above-entitled copending application is an extremely sensitive structure which provides a constant output potential, automatically compensating for variations in the load voltage and additionally in the source potential. To preclude such additional regulation within the converter occasioned by changes in the source or battery potential thereof, the present invention provides a constant DC. voltage level for operation of such equipment.

Prior art attempts to regulate the power supply in such vehicles have included the connection of a variable resistor, such as a carbon pile resistor, in series with the eld coil of the generator operated by the vehicles engine. A solenoid having a plunger actuator to compress or permit expansion of the carbon pile resistor has its winding connected to sense the output of the power supply. In this way the output voltage of the generator can be varied to compensate, to some degree, for fluctuations in the output power level of the system. Of course, the accuracy of such a system is not very high, nor does the accuracy remain constant over a large temperature range. Because of the alternate compression and expansion of the carbon pile resisto-r, such units are subject to aging and wearing out due to contact arcing. These disadvantages render such carbon pile type arrangements unsuitable Where a very high and uniform degree of regulation of the power supply is required.

To provide a well-regulated supply voltage (for example, of the commonly used 28 volt level), the generator field coil (which is normally not center tapped) could have one end thereof connected to the collector or output electrode of each of a pair of power transistors. Such power transistors can then be controlled or rendered alternately conductive by means of a square wave train of signals applied with opposite polarities to the bases or control electrodes of the power transistors. Accordingly the power transistors are alternatively conductive to pass a continuous current through the generator ield winding, thus providing the highest possible lield energy. The wave train can be generated and passed through a preamplifier arrangement, which can be turned on or oii whenever the level of the supply voltage indicates that relay contacts should be closed or opened to effect a l United States Patent 4Chilce 3,676,922 Patented Fels. 5, 1963 regulating function. This switching on and olf can be done at a frequency lower than the frequency of the wave train; thus, when the battery voltage falls, the preamplifier is switched on to pass a train of pulses to the bases ofthe power transistors.

More specifically, a voltage sensitive relay could be used to sense when the vehicle battery provides suflicient voltage to meet the regulation requirements. When the battery voltage is high, there is no output required from the supplemental voltage supply, or converter device, and the relay serves to turn on the preamplifier to pass a train of pulses only when the battery voltage falls. The advantages of simplicity inherent in this system are offset by the production of electrical interference and aging of the relay contacts caused by the repeated opening and closing thereof, and the extent of the error signal deviation required to operate even a very sensitive relay. Obviously the requisite error signal is larger, and the operating time of the relay is slower, than would be the case in a transistorized circuit utilized to eifect control of the converter or other supplemental power supply.

It is an object of the invention to provide a voltage regulator in which an extremely sensitive transistorized control system, which has no moving parts and thus does not produce any radio interference due to contact closure and opening, is utilized to sense the deviation of the vehicle supply voltage from a predetermined level, where the supply voltage includes a battery voltage as supplemented by a rectified potential adjusted by the control system.

It is another object of the invention to provide such a voltage regulator which linds utility in a vehicle, connected so the control system senses deviation of the supply voltage for the vehicle from a predetermined level and regulates the excitation level of the vehicle generator to provide a variable supplemental voltage for aiding the potential of the vehicle battery, thereby to provide a well regulated supply potential.

A voltage regulator system constructed in accordance with the inventive teaching provides a regulated output voltage as a result of augmenting a battery supply potential `by a supplemental potential. A control system is provided which senses the deviation of the instantaneous voltage at the output terminals from the desired regulated potential which should appear thereat. In a preferred embodiment of the invention, the control system furnishes a signal indicative of the deviation from the desired output voltage level to vary the energization of the eld coil of a vehicle generator, thus to Vary the generator output voltage which regulates the boosting of the potential of the vehicle battery to provide the regulated output potential.

The features of the present invention which are believed to rbe novel are set forth with particularity in the appended claims. The invention itself, together with further objects and advantages thereof, may best be understood by reference to the following description taken in connection with the accompanying drawings, in the several figures of which like reference numerals identify like elements, and in which:

FIGURE l is a block diagram illustrating a preferred embodiment of the invention;

FIGURE 2 is a schematic diagram depicting the specific circuitry of certain components of the invention shown in block form in FIGURE l; and

FIGURES 3A, 3B and 3C are graphical representations useful in understanding the operation of the embodiment of the invention shown in FIGURES 1 and 2.

General Description The elements of a preferred embodiment of the inventive control system are indicated in block form in.

FEGURE- l, together with the connections of such system to conventional automotive apparatus depicted within broken line rectangle 16. As there shown the conventional equipment includes a 24-volt battery 12 connected to energize a starter motor 1L.- and to supply power for the vchiclespelectrical system. The vehicle engine 16 is positioned to be driven by a clutch 18 and starter motor 1d. When energized, engine 16 drives crank shaft 2t) and also rotates a drive pulley 22, which rotates belt 24 and thus rotates driven pulley 26 to supply mechanical power to generator 2S. Because of the increased efficiency obtainable at high power levels, a three-phase generator is used. The output level of generator 23 is varied as the amount of energy coupled to ield coil 30 or" the generator is varied. When energized, generator 28 supplies alternating current (AC.) power to a rectitier 32, which converts such energy to D.C. power. Rectitier 32 may -be parallel-connected with battery 12 to aug-ment or boost the yvoltage appearing at the battery terminals.

In accordancewith one aspect of the invention, the novel control system includes a delay stage 34 to which an energizing potential from battery 12 and an operating signal from generator 2S are applied. When generator 2E produces only a low output voltage, below the level of the operating signal, delay stage 34 furnishes a disabling signal to voltage sensing stage 36 which maintains the control system inoperative. As engine 16 reaches idling speed, the requisite operating signal is applied to delay stage 34- to cut off transistor 62 (FIGURE 2) and the disabling signal is removed, thus conditioning voltage sensing stage 36 (and the entire system) for operation. The energizing potential of battery 12 is coupled over an input filter 33 to voltage sensing stage 36. A supply Voltage stabilizer itl and a reference voltage stage 42 are also coupled between input iilter 38 and voltage sensing stage 36. As will be made clear hereinafter, stabilizer 4t) provides a constant operating voltage for voltage sensing stage 36. A temperature control unit 44 energized by battery 12 senses the ambient temperature, and regulates the temperature of the components in voltage sensing stage 36 and'in certain other elements of the inventive control circuit. The voltage sensing circuit need be temperature controlled only for vquick star-ts at very low ambientvtemperatures; otherwise the lcircuit is operable without the temperature control unit or oven.

The output side of voltage sensing stage 36 is coupled through an ampli-lier stage '46, a power switch 48, and a clipper stage t) to iield coil 36 of the generator. The output signal from voltage sensing stage 36 is thus amplitied and applied to lield coil St) to regulate the energization of generator 28. Amplitier 46 is energized from bat- .tery 12, as is a back bias unit 52 for power switch 46.

Although shown as separate stages in the simplied diagram of FIGURE l, supply voltage stabilizer 4u, clipper 5d, and back bias stage 52 may be simple Zener diodes or rectifier units. The general circuitry and the cooperati-on between stages will now'be described in connection with FIGURE 2.

With reference to FIGURE 2, terminals 60 and 61 represent the supply terminals to which equipment in the mobile unit isconnected. A 28 volt potential may be provided to energize the electrical equipment of the vehicle lby the parallel Aconnection yof battery 12 and the output circuit of rectiiier 32, as explained in connection with the simplified showing of FIGURE l. The apparatus of the preferred embodiment shown in FIGURE 2 is connected to operate in such manner that, when the desired 28 volt potential is present at terminals 60 and 61, the potential appearing at the base of first transistor 68 in voltage sensing stage 36 is sufficient to maintain this stage conductive, which causes the second stage of the Schmitt type bistable voltage sensing arrangement:Y to be maintained non-conductive. The various amplier and power switching transistors are also maintained nonconductive, so long as the second voltage sensing transistor 70 is biased to cut-oft.

IDelay stage 3d prevents the second transistor stage 7 il from operating, even if transistor 63 should be cut oif, il' the A.C. output voltage of the generator is too low. When the engine is at cranking speed, there is little output voltage from generator 28, and only a small signal is translated across coupling transiormer 116 and rectiiied in bridge 113 to provide a negative or back-bias potential at base 62h of transistor switch 62. Accordingly the forward bias normally provided vby the emitter and base connections of this stage causes a collector current to ow from transistor 62 over common emitter resistor 8o in voltage sensing stage 34. rIltis current iiow Causes a voltage drop across common emitter resistor di) which provides sufficient back-bias for stage 7d to maintain this stage, and the power boosting system, turned od irrespective of the state of transistor 63.

A resistor 98, series-connected with field coil 3i) between supply conductors 63 and 64, provides a small, steady current through the iield `coil to energize generator 28 at a low level. However, such level is insufficient to provide a signal across transformer 114i sufficient to develop an output potential or operating signal from rectilier bridge 113 of a level sutiicient to cut oit transistor switch 62. The control eiect ot the output potential from generator 28 coupled over transformer 11d and rectified in bridge 113 is determined by the turns ratio in transformer 110` and by the steady state iield current through resistor 9S and iield coil 39 when the engine is only idling. In a preferred embodiment, such turns ratio and resistance value were set so that, when engine 16 is cranked by starter motor 14 over a driving connection from clutch 13, the voltage output from generator 28 does not produce a negative voltage of sufficient level -to cut oti tran-y sistor 62. These values were adjusted so that, when the! engine reached idling speed, the generator output produced a D.C. control voltage at the output terminals of rectifier bridge 113 suiiicient to cut ofi transistor 62 and remove the back-bias `from common emitter resistor caused by iiow of collector current from transistor 62, so that when transistor 68 is subsequently cut oit, such operation is eiective to immediately turn on transistor 7@ and the remaining transistors in the control system. The inclusion of resistor 113 in the secondary circuit of transformer 114i limits the secondary current to a safe value as the engine speed increases farther. Manitestly, if resistor 118 is a non-linear unit such as a thermistor, temperature influences on the threshold operating level of transistor switch 62 can be compensated. t

The switching time of transistor 62- is very tast, in the order of a few microseconds. Accordingly, as soon as the engine appnoaches idling speed, a suiiicient output potential appears across rectiiier bridge 113- and transistor switch 62 is cut off, so that a lower supply potential at terminals 62 and 61 is effective to cut oil" transistor 63 and turn on transistors 7d, 91?-92, and 16o and 162. Thus the iield coil 30 is fully energized to raise the output level of generator 28, which is rectiiied in rectifier 32 yand used to supplement or augment the output of battery 12 to increase the load voltage. This increase is immediately sensed at terminals 6i) and 61 yas applied over Zener diodes 73 and 72 to base 66h of transistor 63. Thus the satisfaction of the regulation requirements is immediately sensed and the control system is Aturned olii as the desired potential (i.e., 28 volts) is reached. As will be made clear in connection with FIGURE 3, the system is thus cycled `on and ott during brief periods, and both the on time (or Vduty cycle) of the system and the duration between Isuccessive conductive periods (or frequency) are functions of the difference in the actual potential at terminals 6i) and 61 due to the load conditions and the desired output potential. Because both duty cycle and frequency are varied, the regulation quality is assured for different engine speeds which would otherwise cause considerable voltage changes because of the nature of tbe generator. The rapid cycling of the system to regulate the potential at terminals 6@ and 61 provides what is, for practical purposes, a constant and well regulated potential at these terminals. The specific system of FIGURE 2 will now be described.

Circuit Descrptz'on-FIGURE 2 Control system 34-52 is energized over a negative conductor 63 and a positive conductor 64 which are connected to input terminals 60` and 61, respectively. An input filter, shown as block 38 in FIGURE l, is connected between conductors 63 and 64 and voltage sensing stage 36, and includes an input impedance element shown yas an inductance 65, which may be replaced by a resistor, connected between terminal 66 and reference voltage stage 42, and a capacitor 67 connected between supply conductors 63 and 64. This filter protects the control system against any malfunction which might otherwise be caused by .the high ripple component and spikes or sharp pulses which appear lin the Voltage iat terminals 6i) and 61. This size of the lter components affects the ripple. If inductance 65 includes a high value of resistance, rand if capacitor 67 is also large, this large RC time constant will produce a high amplitude ripple of low frequency. Conversely, a low RC time constant produces a low amplitude ripple of high frequency.

Voltage sensing stage 36 comprises a pair of transistors 68 and 70, and is energized over negative and positive conductors 63 and 64, respectively.

Transistor 63 is of the PNP type and includes lan emitter 68e, a base 68h, and a collector 68e. Because this transistor is connected in a common-emitter contiguration, emitter 68e is the common electrode, base 68!) is the input electrode, and collector 68e -is the output electrode. In like fashion transistor 70 tis :also of the PNP type fand includes an emitter 70e, a base 7Gb, and ya collector 70C. Bias potential for base 631; of input transistor 68 is provided by a voltage divider arrangement including resistor 71 and Zener diodes 72 and 73, series-connected between positive conductor 64 and negative conductor 63'. Another resistor 75'` is parallel-connected with resistor 71 and diode 72.

Collector 68C is connected over resistor 76 and diode 73 to negative conductor 63; diode 73 reduces the supply potential Iappearing on conductor 63v to a safe value for collector 63e. The junction of resistor 76 and collector 68e is coupled over series-connected resistors 77 and 78` to conductor 64 'to provide bias potential for base 70]) of transistor 7o; base 76h is connected to the junction of resistons 77 and 73. Resistor 80 is connected as the common emitter resistor for emitters 63e and We of transistors 68 and 79. Collector 749C of transistor 76J is coupled over resistors 33, 84 and S5 to negative conductor 63.

As mentioned hereinbefore, transistors 63 and 7o are connected in a Schmitt-type bistable trigger circuit. The bias potential appearing across resistor 71 in the baseernitter circuit of transistor 68 is established by voltage divider arrangement 71-73, with the principal portion of the potential supplied at terminals 6ft yand 61 appearing across Zener diodes 72 and 73. rlhe remainder of the potential appears across resistor 71, and when the potential at terminals 60 and 61 is 28 volts, the bias potential appearing across resistor 71 is suiiicient to maintain transistor 68 conducting. The collector current of this stage flows through resistor 76, causing a voltage drop thereacross which reduces the forward bias appearing across resistor 7S in the base-emitter circuit of transistor 79; the voltage drop .across common emitter resistor 8i) provides a back bias for transistor 70, thus maintaining this transistor non-conductive. When the potential at terminals 6i) and 61 is decreased sufciently, the forward bias for transistor 68 is decreased by the amount required to cutoff this transistor. as transistor 68 is cut olf,

the back-bias for transistor 70 formerly contributed by current iiow from transistor 68 through common emitter resistor S6 is removed. As transistor 68 ceases conduction, the voltage drop across resistor 76 is likewise decreased, the potential changes in this voltage divider arrangement (73, 76, 77, 78) providing a forward bias in the emitter-base circuit of transistor 70; if transistor 'switch 62 has been cut off, this forward bias is sufficient to cause transistor 70 to conduct. The switching action between the conductive and non-conductive conditions of these two transistors is weil known and understood in the art.

The switching of tnansist-ons 68 and 70 between the conductive and non-conductive states is facilitated, and thus the sensitivity of the inventive control system is further increased, because Zener diode 73 is connected in the voltage-divider arrangement (73, 76, 77 and 78) to which base 7Gb of the second transistor is connected. Whereas the terminal voltage at terminals and 61 may be 28 volts, a negative potential across resistor 71 of, for example, only 2 volts is suiiicient to cause transistor 68 to conduct and a potential difference of, for example, 0.3 volt is sufficient to elfect non-conduction of transistor 63. Manifestly if a simple resistive voltage divider were connected between supply conductors 63 and 64 to pass terminal voltage uctuations to the input circuit of transistor 68, only a small voltage fluctuation, insufficient to effect the desired switching, would appear in the input circuit of the voltage sensing stage. However, with the utilization of Zener diodes 72 `and 73, series-connected with resistor 71 so that a current suicient to maintain their operation well within the Zener or constant voltage region flows through these diodes, a constant potential drop appears 'across diodes 72 and 73. Accordingly substantially all of the voltage fluctuations appearing at terminals 66 and 61 are transferred to base 68b of transistor 63, and, because diode 73 is `also in the voltage divider circuit to which base 7G51) of second switching transistor 76 is connected, a similar action is effected for this transistor. Thus voltage sensing stage 36 exhibi-ts a very high sensitivity (in practice a few hundred m-illivolts) by reason of the utilization of constant-potential Zener diodes to transfer nearly all of the terminal voltage fluctuations to the error-sensing portion of the control system.

A supply voltage stabilizing Zener diode 40 is connected between positive conductor 64 and `a point in the voltage-divider network which supplies operating potential for collector 76C of transistor 70, and a capacitor 86 is parallel-coupled with diode 4f) to protect the diode against overvoltage spikes or pulses. Thus the second transistor is also operated from a stable voltage, and Zener diode liti also serves to drop the supply potential for the first transistor of amplifier 46 to a desired level.

Amplifier 46 includes an NPN type transistor 90 and a pair of PNP type transistors 91 and 92. Transistors 91 and 92 are connected in an emitter-follower configuration to provide a low-impedance driver source for power switching stage 43, First transistor 9i) of the amplifier is an NPN type to facilitate switching the ampiier on responsive to conduction of second transistor in the voltage sensing stage.

Specifically, transistor includes an emitter 90e conected to the junction of resistors 84 and 35, and a base gob connected to the junction of resistors 83 and 84 in the voltage-dropping arrangement connected between collector 76e of transistor 70 and negative conductor 63. Collector 99C is connected over resistors 97 .and 93 to positive conductor 64, and the junction of resistrs 97 and 93 is connected to base 91b of transistor 91.

Coilector 91C of transistor 91 is connected over a resistor 9d to negative conductor 63. Emitter 91e of transistor 91 is connected both to base 92]:v of transistor 32, and over a resistor 95 to positive conductor 64. Collector 92C of transistor 92 is connected over a resistor 96 -to negative conductor 63, .and emitter 92ev is 1 connected both to base web of transistor tot) in power switch d8, and also over resistor 101 to positive conductor 64.

If the generator output is sucient so that transistor switch 62 is cut oit", the back-bias on resistor Si) caused by collector current from 62o is removed and the system is ready for operation. In the inoperative condition of the control system (i.e., with .a full 28 volt potential at terminals di) and d1), transistor GS is conducting and transistor 70 is cut oi in voltage sensing stage 36, transistors 91E-92 in amplifier section d6 are cut of?, and transistors le@ and 162 in power switch ld are also cut off. As the voltage at supply terminals dil and e1 decreases from 28 volts, transistor 68 is cut oil" and transistor 70 becomes' conductive, as explained above. Collector current from transistor 70 flows through resistors S3, 84 and S5; the potential at base 991) of transistor 9i) goes more positive and this transistor is switched on. Accordingly the collector current tlowing through resistors 97 and 93 causes the potential at base 91h of transistor 91 to go more negative, turning on transistor 1 and effecting current ilow through emitter resistor.

95 `of this stage. Such current ow also causes a more negative potential to appear at base 92b of transistor 92 which is also immediately rendered conductive, and current flows through emitter resistor 101, transistor 92, and collector resistor 96 of this stage.

Power switching stage 48 includes a second transistor 102 parallel-connected with lirst transistor Idil. Emitters little and 102e of these two stages are coupled together, and over a power diode 52 to positive conductor 6d. Diode 52 may be of the silicon junction type and is connected to provide back bias for the power switching stage when it is non-conductive, because such a diode does not conduct until about 0.5 volt is applied thereacross. Collector 100C of transistor 10G is connected over a dropping resistor 103 to a common point, and collector 102C of transistor 102 is connected over resistor 161i to such common point; eld coil 30 of generator 23 is coupled between such common point and negative conductor 63. vUse of separate resistors 193 and 104, and adjustment of their individual resistance values, enables transistors 1st) and 102 to share equal portions of the load current. A de-spiking diode 5@ is parallel-connected with field coil Sil to protect power switching transistors 1li@ and 162 against voltage pulses or spikes developed across coil 3i? as the current therein is rapidly cut off.

When transistor 92. becomes conductive, its emitter current flows through resistor 1M and causes the potential at bases 1Mb and 1552!: of transistors lltlt and 102 to go more negative, causing these transistors to conduct, thus translating power through eld coil 3d and increasing the output of generator 28. Three separate conductors are shown at the output side of the generator because a three phase A.C. generating system may be used to provide a high power output with greater eiliciency than is attained in a single phase system; rectifier 32 is connected to rectify this A.C. power to produce D.C. power for augmenting the DC. battery Voltage.

Temperature control unit dd is shown encompassing voltage sensing stage 36 including Zener diodes '72 and 73, and a heating resistor 1&5 which is series-connected with .a bimetallic or thermostatic switch 106. Elements 165 and k1de are connected between positive conductor 6d and negative conductor 63. As the temperature within unit or oven Vi4 falls below a preset level, thermostatic switch 1616 is closed through deection of the birnetallic element in a well known manner and current hows through resistor 105 to raise the temperature within the space. As the temperature reaches the desired level, thermostatic switch 106 is opened to remove the energy supply from the heating resistor, and continued operation of switch 106 in this manner maintains constant the temperature level of the various elements within temperature control unit 4d. Thus there is no distortion if of the indications to voltage sensing stageo by reason of the temperature increases and decreases of the various components in this stage and connected to this stage. instead, only the voltage at supply terminals dit .and 61, as coupled over conductors 63 and 64 to voltage sensing stage 36, determines the operation within this stage.

The input side of delay stage 3d includes a coupling transformer 11d which has a primary winding 111 coupled to two of the three phase conductors of generator 23. The lower terminal of secondary winding 11.2 of transformer 119 is connected directly to the lower input terminal of a bridge rectiiier 113, including four rectihers 11d-117, and the upper terminal of secondary winding 112 is coupled over a resistor 118 to the upper input terminal of bridge 113. Each of rectitiers 114-117 includes an anode referenced by letter a and a cathode designated by letter b. One output point of bridge rectifier 113, at the junction of anodes 114cand 115m, is coupled over series-connected resistors 12d and 1231 to positive conductor ed. A transistor switch d2 includes an emitter 62e, a base 62h, and a collector ec; base 62h is connected to the junction of resisto-rs 12d and 121. Connections are also made from the second output terminal over conductor 122 to negative supply terminal ed, and to emitter 62e of transistor switch 62.

When the output voltage level of generator 28 is 10W (as when the engine is at cranking speed), there is only a slight voltage potential appearing across the output terminals of rectifier bridge 13, and so only a negligible negative voltage is supplied to base 62]: of transistor switch 6,2. Accordingly, with the positive bias applied `from the junction of resistors 12.0 and 121 to base 6211, and the negative potential applied from terminal d0 to emitter 62e of the transistor, the emitter-base circuit of transistor switch 62 is forward-blassed and this transistor conducts. Collector current flows from 62C over conductor d1 and through common emitter resistor S0 to positive conductor 64, establishing a back-bias across emitter resistor di) of a level sulicient to maintain transistor '70 non-conductive irrespective of the action of rst transistor 6d in voltage sensing stage 36. rl'hus, delay stage 3d eilectively disables voltage sensing stage 36, and may be said to apply a disabling signal to the control system to maintain such system inoperative until an output voltage of appreciable level appears at the output conductors of generator 2S.

One purpose of delay stage 3d is to assure that the engine has reached a reasonable speed, for example, at least idling speed, before the load of the generator is added to the engine. Without a delay stage, the control system would operate as soon as starter motor 14 (FIG- URE. l) was energized to drive engine 16. Thus the control system would be energized and pass current through tield coil 31B, placing a considerable counter torque on the drive system and causing slippage of the belts. Delay stage 34 not only obviates this diiculty, but also protects power switch stage 48 from drawing continuous current at a high level if the ignition key of the vehicle in which the control system is installed is turned on without cranking the engine to produce a usable generator output voltage. Such turning of the key might be accidental, or may occur incertain automotive systems in which the electrical system can be energized to operate equipment (i.e., radio, lights, etc.) even when the engine is not turning over.

As the engine is cranked and reaches idling speed, the generator output potential increases; the Output voltage of one phase is applied across primary winding 111 of transformer 11d 4and the potential which appears across secondary winding 11'2 is rectilied in bridge circuit 113. Resistor 118, connected in the secondary circuit of transformer 11d, protects this circuit against excessive current ilow under conditions of increasing generator output.

' rl`he polarity of the output voltage from rectier bridge 113 is negative at the junction of anodeslda and 116:1;

this voltage is applied over resistor 120 to base 62h of transistor switch 62. As this voltage increases to a level sufficient to overcome the forward bias normally applied to the emitter-base circuit of the NPN-type transistor switch, transistor 62 is cut olf and collector current ceases to iiow, removing the high back-bias previously applied across common emitter resistor 80 of transistors 68 and 7d by reason of such current ow. With the removal of the high back-bias formerly contributed by the ow of collector current over conductor S1 and common emitter resistor 80, transistor 70 is conditioned for operation to the conductive state immediately upon cut off of transistor 63 by a `decrease in the potential appearing at load terminals 60 and 61. As soon as second transistor 7()l in voltage sensing stage 36 is conductive, the remaining transistors in the system 943-92, 100 and 102 become conductive and pass additional current through tiield coil 30, raising the energization level of generator 28 and increasing its output. Thus, before the output voltage of generator 28 is high enough to produce a suiciently negative potential at the output of bridge rectifier 113 to cut off transistor switch 62, the only excitation for field coil 30 is the minimum current ow provided from supply conductor 64, over resistor 98, field coil 36, to supply conductor 63. Thus a large counter torque is not placed upon th-e drive system during the initial cranking of the engine. Those skilled in the art will recognize that an alternative to the electrical delay stage 3d is a system for automatically regulating the tension of drive belt 24 (FIGURE 1) to insure that the load represented by generator 28 is not placed upon the engine during acceleration.

' In one embodiment of the invention, transistor switch 62 and its associated circuitry was selected to provide a turn-on voltage ot -l-0.8 volt; that is, when the baseernitter voltage reached |0-8 volt, transistor 62 became conductive. This transistor switch became non-conductive at a turn-oit voltage of volt. When the engine was at cranking speed, the output level of generator 28 was set so that only about 0.3 volt was applied across primary winding 111 of transformer 112; accordingly, at this engine speed transistor 62 remains conductive and a disabling signal is applied over conductor 31 to prevent operation of the control system. When the engine attained idling spe-ed, a signal of approximately 2 volts was applied to primary winding 111, which developed a negative voltage of sumcient level at the output terminals of rectifier bridge 113 to render transistor switch 62. nonconductive, removing the disabling signal fro-m conductor 81 and resistor Sli and thus conditioning the control system for operation.

System Operation- Figure 2 As the ignition key (not shown) is turned, starter motor 14- (FIGURE l) is energized and clutch 18 effects a driving connection between starter motor 14 and engine 16. At this time the requisite DC. potential is app-lied from supply terminals 6i) and 61 (FIGURE 2) to voltage sensing stage 36 of the invention, but the control system is still inoperative because the output voltage of generator 28 is still insufficient to cut off transistor switch 62 and remove the disabling signal from the control system. As the output of generator 23 increases, the potential applied to primary winding 111 of transformer 11d also increases, and the output voltage of bridge 113 increases to provide a biasing potential at base 62h, suflicient to cut oft" transistor 62, and this switch is turned olf to discontinue application of the disabling signal to the control system. At this time, assuming that the supply potential at terminals 60 an-d 61 is slightly below 28 volts, there is insufficient potential applied at base 68b of transistor 68 to maintain this transistor conductive and so it is cut off. Accordingly the potential dropped across resistor 76 is decreased, causing the potential at base 70h of transistor '70k to go more negative, turning on transistor 1G 76, and sequentially turning on each of the transistors in amplifier 46 as explained hereinbefore. Conduction of transistor 92, the last transistor in amplifier 46, develops a sufcient potential across bias resistor 101 in power switch 4S to turn on transistors 100 and 192. Transistors 101i and 162 thus conduct, translating current through eld coil 30 and increasing the energization of generator 28 which instantly effects an increase in the supply potential at terminals 60 and 61. This potential increase like- Wise raises the bias potential across resistor 71, and transistor 68 is 'again turned on and each of the remaining transistor stages is cut off so that there is now only the minimum energization of field coil 30. As the voltage at terminals 60 and 61 varies, the control system is rapidly switched on and off and the energization of field coil 3G is simultaneously varied; this periodic energization of the field coil is depicted in the shaded areas of the pulse waveforms shown in FIGURES 3A, 3B and 3C.

When transistor 68 is cut off, transistors 70, 90, 91, 92, and 102 conduct to supply power to field coil 3ft. The conduction of these six transistors is indicated by the shaded areas in FIGURES 3A-3C. In FIGURE 3A, with a low battery output voltage and a heavy generator load, the pulse duration is of a substantial period prior to the time at which the sensing unit turns off the control system. The pulse duration or on time of the system, measured as the current flow between emitter and collector of power transistors 100 and 10'2, was approximately 34 milliseconds, and the control system was cut orf for approximately 8 milliseconds, whereby a series of relatively long duration pulses is produced by the control system. As noted hereinbefore, both the pulse length or on time of the system and the interval between pulses are dependent upon the battery output level and the load on the vehicle generator. Because the pulses are of a duration measured in milliseconds, for example only 34 milliseconds as shown in FIGURE 3A, many pulses are transmitted -to field coil 3l) during a single second Iand so the output voltage at terminals 60 and 61 is stabilized at what, for practical purposes, is a constant supply potential.

With a decrease in the load on the generator and a somewhat higher battery output voltage, the on time of the contro-l system is reduced and the time interval between successive pulses or conductive periods of the system is similarly increased, as depicted in FIGURE 3B. Under the conditions there shown the system is conductive for an interval of approximately 17 milliseconds and is cut off for an interval of approximately 28 milliseconds. FIGURE 3C indicates the system operation when the battery output supplies practically the entire potential required at terminals 60 and 61 with a light load on the generator. The consecutive pulses or on times of the system there depicted are approximately 8 milliseconds and 5 milliseconds in length, with a duration of about 60 milliseconds between successsive pairs of pulses. No matter the particular pulse duration or repetition rate of the pulses indicating the conductive time of applicants novel control system, the effect is to provide a substantially constant output potential at terminals 60 and 61 by reason of the modulation of -the on time of the control system which supplies the variation of the energization of field coil 30 necessary to produce such a constant supply potential.

The control system is thus on continuously (transistors 101i and 102 fully saturated) as long as the voltage at terminals 60 and 61 is less than or equal to 27.8 volts, and is olf continuously whenever the voltage at terminals 60 and 61 is equal to or greater than 28.0 volts. When saturated the power transistors dissipate approxi- 'mately three watts, as contrasted to known gradually changing regulating systems wherein about 45 watts is dissipated.

Overload protection is provided by the generator itself because its field. winding saturates at acertain current emessa level, thereby limiting the current ow. This saturation level is sufficiently low to insure that the transistors are not driven into the runaway state.

ln determining the eiiiciency of a voltage regulator including the novel control system, a voltage of 27.5 volts was applied to terminals 6G and 6l, and a current ot l amperes was passed through iield coil 3u. The power in iield coil Sil was 375 watts, and the total power drain of the power stage Was 438 watts; thus the eiiiciency was 86%.

it can be shown that, if iield coil 3i) were tapped at one or more points and the output circuits of transistors 91 and u?. were connected to such points, the power now lost in collector resistors 94 and 96 can be made an `active part of the energy in 'field coil 30. Moreover, for applications requiring less lield power, transistor lull and balancing resistors 103 and 104 can be removed. The overall efficiency of a regulator thus modiiied can be increased to 3S-97%, for the principal power losses in the illustrated embodiment occur in resistors 96, 103, and 104. Such a modified regulator could be enclosed within a smaller carrying case, for the thermal outputs of the major heat sources are either eliminated or reduced.

The switching speed of the transistors, especially in the power stage, is about 30 microseconds. When compared to the thermal response time of about milliseconds, the thermal safety factor (about 700 times slower than the ,switching time) is manifest. There was no trace of voltage spikes or pulses during system tests, giving promise of long life expectancy for the invention.

Summary ri`he embodiment of the invention disclosed herein is an accurate and efficient control system for use in a voltage regulator to provide an accurate, well-regulated supply voltage. Such a regulator unit can be mounted in front of the radiator in a truck or other automotive vehicle, thus providing cooling of the control system components. Such cooling, in conjunction with the temperature control of the voltage regulator stage and associated components, provides for highly accurate operation of the system and effects regulation of a supply voltage within f0.2 volt. This is a marked improvement over prior art systems, such as the carbon pile regulator systern, which provides regulation within approximately iLS volt. `One reason for the substantial increase of sensitivity is the use of a reference voltage state (e.g., stage 42 in FIGURE l) to provide a constant voltage drop, thus transferring substantially all of the source voltage deviations to the bases of the voltage sensing transistors. r[he transistors of the inventive control system are cycled, being switched on and oft at a rate related to the deviation of the output voltage from a desired value, to supply the proper average power to the generator coil to stabilize the supply voltage. Because the transistors conduct only when the vehicle battery requires augmenting by increasing the energization of the generator, the life of the transistors in the system is extended. A delay stage can be incorporated as taught in conjunction with the preferred embodiment to insure that an additional load is not placed on the vehicles engine by energizing the field coil of the generator before the engine -has come up to speed. Those skilled in the art will recognize that a transistor switch such as that incorporated in the delay stage may replace the Schmitt trigger cir-cuit of the voltage sensing stage.

Although a particular embodiment of the linvention has been shown and described, it is manifest that alterations and modilications may be made therein, and it is intended in the appended claims to cover all such modiiicatio-ns and alterations as may fall Within the true spirit and scope of the invention.

What is claimed is:

l. For use in a voltage regulator for a generator having an input circuit including a field coil and an output circuit coupled to a vehicle battery for augmenting the potential appearing at the battery terminals, the combination of a voltage sensing stage coupled across said battery terminals operative in response to minute deviations ofthe battery voltage from a desired value to provide output pulses to said field coil which vary in duty cycle and irequency with ditlerent variations `of the voltage from said desired value; and control means connected between said voltage sensing stage and said iield coil for regulating the energization level of the held coil in response to the presence and absence of said pulses, whereby the output voltage of said generator which augments said battery voltage is simultaneously adjusted to provide a regulated output potential at said battery terminals. Y

2. For use in a voltage regulator for a generator having an input circuit including a ield coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination of a transistorized Voltage sensing stage coupled to said battery terminals for providing a control signal in response to deviation oi the battery voltage from a desired value; a reference voltage stage, coupled between said battery terminals and said voltage sensing stage, for producing a constant potential drop across said reference voltage stage whereby substantially the entire voltage deviation at said battery terminals is applied directly to said voltage sensing stage; and a transistorized power switching stage coupled between said voltage sensing stage and said -iield coil for regulating the energization level of the iield coil in response to the presence and absence of said control signal, whereby the output voltage of said generator which augments said battery voltage is simultaneously adjusted to provide a regulated output potential at said battery terminale.

3. For use in a voltage regulator for a generator having an input circuit including a eld coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination of a voltage sensing stage coupled to said battery terminals for providing a control signal in response to deviation of the battery voltage from a desired value; a delay stage coupled to said generator and to said voltage sensing stage operative to generate adisabling signal whenever the output voltage of said generator is below a preassigned level, and means for coupling the disabling signal to said voltage sensing stage to prevent the operation thereof; and control means connected between said voltage sensing stage and said field coil, for regulating the energization level `of the field coil in response to the presence and absence of said control signal Whenever the output voltage of said generator is at least equal to said preassigned level, to thereby adjust the output voltage ot said generator which augments said battery voltage and thus provide a regulated output potential at said battery terminals.

4. For use in a voltage regulator for a generator having an input circuit including a field coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination of a transistorized voltage sensing stage coupled to said battery terminals for providing a control signal in response to deviation of the battery voltage from a desired value; a temperature control unit enclosing said voltage sensing stage and coupled to said battery terminals, for maintaining said voltage sensing stage at a substantially constant temperature; and a transistorized power switching stage, coupled between said Voltage sensing stage and said iield coil, for regulating the energization level of the iield coil in response to the presence and absence of said control signal, to thereby adjust the output voltage ot said generator which augmente said battery voltage and thus provide a regulated output potential at said battery terminals.

5. For use in a voltage regulator for a generator having an input circuit including a field coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination ofa voltage sensing stage including a first and a second transistor couplied in a trigger circuit t-o provide non-conduction of said second transistor when said first transistor is conductive and to provide conduction of said second transistor when said first transistor is non-conductive, and means coupling said first transistor to said battery terminals to effect nonconduction of saidfirst transistor in response to decrease of the battery voltage below a predetermined value; and a transistorized power switching. stage, coupled between the second transistor of said voltage sensing stage and said -field coil, for supplying energy to said yfield coil in response to conduction of said second transistor, tol therebyfadjust the output voltage of said generator which augments said batteryjvoltagerand thus provide a regulated output potential at sai-d battery terminals.

-6. Por use in a' voltage regulator for a generatorjhaving an input circuit including a fieldcoil'and an output' Acircuit coupled to a battery: for augmenting the potential appearing'at the battery terminals, the combinationof a voltage sensing stage including a'zfirstganda second tranf sistor coupled in a trigger circuit to provide non-conduction of said second transistor when said first transistor is conductive andto .provide 'conduction of said' second 'transistor` whensaid first transistoris non-conductiveg a reference voltage stage including a Zener diode coupled between said first transistorand said battery terminals, for producingk a'constant potential drop across` said Zener diodeand. transferring substantially the entire voltage deviation at said battery terminals directly to said voltage sensing stage, and for effecting' non-conduction of said first transistor land conduction of said second transistor in response to decrease of the battery voltage below a'predetermined value; and a transistorized polwer switching stage, coupled between the second transistor of said voltage sensing stage and said eld coil, for supplying energy to Asaid field coil in response to conduction of said second transistor, to thereby adjust the output voltage of said generator which augments said battery voltage andthus provide a regulated output potential at said battery ter` minals.

7. For use in a voltage regulator for a generator having an input circuit including a eld coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination of a voltage-sensing stage including a first and a second transistor, each having input, output, and common electrodes, coupled in a trigger circuit to provide nonconduction of said second transistorwhen said first transistor is conductive and to provide conduction of said'second transistor when said first transistor is non-conductive; means for transferring substantially the entire voltage deviation appearing at'said battery terminals to'said voltage-sensing stage comprising a series circuit including aresistor coupled to one ofH said battery terminals, areference voltage. stage 'includingal Zener diode coupled between said resistor and-the other of said battery terminals, and means coupling the junction of said resistor and said reference voltage stage to the input electrode of said first transistor; and a transistorized power switching stage, coupled between the second transistor of said voltage sensing stage and said field coil, for supplying energy to said field coil in response to conduction of said second transistor, to thereby adjust the output voltage of said generator which augments said battery voltage and thus provide a regulated output potential at said battery terminals.

8. For use in a voltage regulator for a generator having an input circuit including a field coil and .an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination of a voltage sensing stage including a first and a second transistor coupled in a trigger circuit to provide non-conduction of said second transistor when said first transistor is conductive and to provide conduction of said second transistor when said first transistor is non-conductive, andrmeans coupling said first transistor to said battery terminals to effect non-conduction of said first transistor in response to decrease of the battery voltage below a predetermined value; a delay stage including a transistor switch coupled to said voltage sensing stage to supply a disabling signal thereto, biasing means coupled to said transistor switch to effect conduction thereof and thus disa-ble said voltage sensing stage, and rectifier means coupled between said generator and said transistor switch to effect cutoi of said transistor switch when the output level of said generator reaches a preassigned level and thus enable said voltage sensing stage; and a transistorized power switching stage, coupled between the second transistor of said voltage sensing stage and said field coil, for supplying energy to said field coil in response to conduction of said'second transistor', to thereby adjust the output voltage of said generator which vyaugments said battery voltage and thus provide a regulated output pot'ential at said battery terminals. i

' 9. For use in alvoltage'regulator for a generator having an input circuit including a field coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination of a voltage-sensing stage including a first and a second transistor, each of which comprises base, emitter, and collector electrodes, coupled in a trigger circuit including a common emitter resistor having one end thereof coupled to the emitter of each of said first and second transistors to provide a back-bias voltage for said second transistor responsive to conduction of said first transistor, and means coupling said first transistor to said battery terminals to effect non-conduction thereof and conduction of said second transistor in response to decrease of the battery voltage below a predetermined value; a delay stage including a transistor switch having input, output, and common electrodes, means coupling the output electrode of said transistor switch to said one end of said common emitter resistor to supply a back-bias voltage of a level sufiicient to maintain said second transistor non-conductive irrespective of the operation of said first transistor, fbiasing means including a voltage divider arrangement coupled to the input electrode of said transistor switch to effect conduction thereof and thus maintain the disabling back-bias potential across said common emitter resistor, and means including a transformer and a recti- `filer bridge coupled between said generator and said transistor switch to effect cut-ofi of said transistor switch when the output level of said generator reaches a preassigned level and thus remove the disabling back-bias potentlal from said common emitter resistor to enable operation of sald voltage-sensing stage; and a transistorized power switching stage, coupled between the second transistor of said voltage-sensing stage and said field coil', for supplying energy to vsaid field coil in response .to conduction of said second transistor, to thereby adjust the-output voltage of said generator which augments said battery voltage and thus provide a regulated output potential at said battery terminals.

10. For use in a voltage regulator for a generator having an input circuit including a field coil and an output circuit coupled to a battery for augmenting the potential appearlng at the battery terminals, the combination of a volt-age sensing stage including a first and a second transistor coupled in a trigger circuit to provide nonconduction of said second transistor when said first transistor is conductive and to provide conduction or said second transistor when said first transistor is non-conductive, and means coupling said first transistor to said battery terminals to effect non-conduction of said first transistor in response to decrease of the ybattery voltage below a predetermined value; an amplifier stage including at least one transistor amplifier coupled to said second transistor to effect conduction of said transistor amplifier responsive to conduction of said second trankby adiust the output voltage of said sistor; and a transistorized power switching stage, coupled between said amplifier stage and said eld coil, for s upplying energy to said iield coil in response to conduction of said transistor amplifier, to thereby adjust the output voltage of said generator which auginerits said battery voltage and tnus provide a regulated output potential at said battery terminals.

1l. For use in a voltage regulator for a generator having an input circuit including a iield coil and an lout.- put circuit coupled to a battery `for augmenting the potential appearing at the battery terminals, the combination of a voltage-sensing -stage including a first and a second transistor coupled in a trigger circuit to provide non-conduction of said second transistor when said firstl transistor is conductive and to provide conduction of said second transistor when said first transistor is non- Vconductive, and means coupling said iirst transistor to said battery terminals to eitect non-conduction of said first transistor in response to decrease of the 'battery voltage below a predetermined value; and a power switching stage, including at least one transistor having an input circuit coupled to the second transistor' of said voltage-sensing stage and an output circuit coupled to said field coil, for passing'current through said field coil in response Vto conduction of said second transistor, to thereby adjust the output voltage of said generator which augments said battery voltage and thus provide a regulated output potential at said battery terminals.

12. For use in a voltage regulator for a generator having an input circuit including a field coil and an Output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the .combination of a voltage-sensing stage including a irst and a second transistor coupled in a trigger circuit to provide non-conduction of said second transistor when said iirst transistor is conductive and to provide conduction O said second transistor when said first transistor is nonconductive, and means coupling said first transistor to said battery terminals to effect non-conduction of Said first transistor in response to decrease of the battery voltage below a predetermined value; and a power switching stage, including a pair of parallel-connected transistors having an input circuit coupled to the second transistor of said voltage-sensing stage and a separate balancing resistor connected between the output circuit of each of said parallel-connected transistors and said iield coil, for passing current through said field coil in response to conduction of said second transistor, to theregenerator which augments said battery voltage and thus provide a regulated output potential at said battery terminals.

13. For use in a voltage regulator for a generator having an input circuit including a iield coil and an output circuit coupled to a battery for augmenting the potential appearing at the battery terminals, the combination or a voltage-sensing stage including a iirst and a second transistor coupled in a trigger circuit to provide 16 non-conduction of said second transistor when said iirst transistor is conductive and to provide conduction of said second transistor when said first transistor is non-conductive, and means coupling said irst transistor to said battery terminals to effect non-conduction of said iirst transistor in response to decreasefof the battery voltage below a predetermined value; and a power switching stage, including a pair of paralici-connectedy transistors each having input, output, and common electrodes, means coupling each of said input electrodes to said second transistor in said voltage sensing stage to effect conduction of said parallebconnected transistors responsive to conduction of said second transistor, a iirst balancing resistor coupled between said iield coil and the output electrode of one of said parallel-connected transistors, and a second balancing resistor coupled between said iield coil and the output electrode of the other of said parallel-connected transistors, -whereby conduction of said parallel-connected transistors eitects current flow through said field coil, to thereby adjust the output voltage of said generator which augments said battery voltage and thus provide a regulated output potential at said battery terminals. f

14. Acontrolsystem according to claim 13 and'furtlier comprising: a bach-bias diode coupled between a point.

of reference potential and the ,common electrode oi cach of the parallel-connected transistors in the power switching stage; and a clipper diode parallel-coupled with said field coil to prevent damage to the transistors in the power switching stage when the current throughthe iield coil is rapidly cut od.

15. For use in a voltage regulator `ior a generator having `an input circuit including a eld coil andan out; put circuit coupled to a battery for augmenting the potential rappearing at Ythe battery terminals, the combi-l nation of a transistorized voltage sensing stage; a reference voltage stage coupled between said voltage-sensing stage'and said battery terminals to transfer substan tially the entire voltage deviations appearing at the battery terminals to said voltage-sensing stage; a transistorized amplier stage coupled to saidvoltage-sensing stage; a transistorized power switching stage including an input circuit coupled to said amplifier stage and an output Vcircuit coupled to said field coil, for `passing current through said eld-coilito adjust the output voltage of said generator which augments said battery voltage and `thus provide a regulated output potential at said battery terminals; and a delay stage, coupled between said geuerator and said voltage-sensing stage, operative to apply a disabling signal to said voltage sensing stage until the output voltage of said generator reaches a preassigncd level.

References Cited in the tile of this patent sommer June as, i959 

1. FOR USE IN A VOLTAGE REGULATOR FOR A GENERATOR HAVING AN INPUT CIRCUIT INCLUDING A FIELD COIL AND AN OUTPUT CIRCUIT COUPLED TO A VEHICLE BATTERY FOR AUGMENTING THE POTENTIAL APPEARING AT THE BATTERY TERMINALS, THE COMBINATION OF A VOLTAGE SENSING STAGE COUPLED ACROSS SAID BATTERY TERMINALS OPERATIVE IN RESPONSE TO MINUTE DEVIATIONS OF THE BATTERY VOLTAGE FROM A DESIRED VALUE TO PROVIDE OUTPUT PULSES TO SAID FIELD COIL WHICH VARY IN DUTY CYCLE AND FREQUENCY WITH DIFFERENT VARIATIONS OF THE VOLTAGE FROM SAID DESIRED VALUE; AND CONTROL MEANS CONNECTED BETWEEN SAID VOLTAGE SENSING STAGE AND SAID FIELD COIL FOR REGULATING THE ENERGIZATION LEVEL OF THE FIELD COIL IN RESPONSE TO THE PRESENCE AND ABSENCE OF SAID PULSES, WHEREBY THE OUTPUT VOLTAGE OF SAID GENERATOR WHICH AUGMENTS SAID BATTERY VOLTAGE 